The invention relates to a safety belt buckle having an electrical switch therein to detect insertion of a tongue plate into the buckle frame.
It is well known for a safety belt buckle to include an electric switch which is actuated by insertion of a tongue plate. Such switches are used in conjunction with buzzers or other warning devices which sound when an occupant of an automobile has not buckled his seat belt. One such switch is described in U.S. Pat. No. 4,163,128, which is assigned to the assignee of the present invention.
A switch in a safety belt buckle should be capable of operation for a period of several years without maintenance while subjected to such adverse environmental factors as dust, temperature extremes, excessive humidity, etc. Dust or corrosion may cause moving parts in a switch to bind to prevent opening or closing thereof, or may interrupt current flow between the contacts. Thus, the switch should be capable of repeated opening and closing without being rendered inoperative by dust, corrosion, or other particulate matter on the contacts. To meet specifications, the switch must be cycled thousands of times under adverse dust, temperature, humidity and other environmental conditions. Also, the switch should be capable of withstanding impact loads applied to the buckle without failure.
It is generally desirable for a safety belt buckle to be compact and lightweight. Accordingly, a switch for use in a safety belt buckle should also have these characteristics. It is also desirable that a buckle be capable of assembly and with relatively little labor, and accordingly it is desirable that the switch not add greatly to the labor involved in buckle assembly. In the past, switches have been generally been assembled by separate installation of each of their various components during assembly of their associated buckles, which is relatively time consuming.
In addition to assembly costs, the cost of the switch itself must be commercially acceptable for manufacture in the millions used in vehicles. Thus, the seat belt switch must meet stiff operational specifications, be readily assembled, and be a low cost switch.